The present invention is in the field of offset printing, decorating or coating of cylindrical objects such as beverage containers formed of aluminum or other material. Even more specifically, the present invention is directed to new and improved apparatus and method for providing a base coat on a container onto which a label-like design providing both aesthetic appeal and information as to the contents of the container is subsequently printed by an offset process. Even more specifically, the subject invention is directed to a new and improved skip-print method and apparatus for preventing contact of an offset blanket with a mandrel on which a container would normally be positioned for receiving ink from the blanket. The prevention of blanket contact with the mandrel occurs in response to the detection of the absence of or mispositioning of a container on the mandrel as the mandrel is being moved upstream of and toward the printing position. Another aspect of the invention is the provision of improved ink fountain roll control means, ink cooling means and ink leakage prevention apparatus.
The beverage container industry has previously employed coating means for coating the exterior of beverage cans fed into position on mandrels mounted on a turret concentrically with respect to the rotational axis of the turret and being equidistantly spaced circumferentially of the turret with respect to each other. Base coating materials employed in providing a base coat to the outer surface of the aluminum or other metal of which the containers are formed have employed rotary devices which receive the coating material from a reservoir and which have rotary roll surfaces for directly applying the paint-like relatively viscous base coat material to the outer surface of the containers as they move into contact with the rotary roll surfaces.
Malfunctions sometimes result from the failure of a container to be positioned on a mandrel or by the mispositioning of a container on a mandrel upstream of the printing or coating location so that when such a fully or partially nude mandrel moves into the printing position, its nude surface is coated with either base coat material or with ink, depending upon the particular operation being performed at that work station. In any event, the result is that subsequent containers positioned on such mandrel are contaminated and must be discarded if the containers are intended for the receipt of a beverage or food product. Moreover, the cleanup of such contaminated mandrel is time consuming and excessively expensive because of down time for the equipment which will normally process hundreds of cans each minute.
Concern with the foregoing problem has resulted in the provision of various devices for preventing the application of base coat material or ink to such a naked mandrel. Generally speaking, such devices use apparatus capable of detecting the absence of a container at a location upstream of the coating o printing station with the detection devices frequently being proximity sensors or photoelectric sensors or the like. Such sensors provide an electrical signal which is used for deactivating the coating or printing means in a variety of ways. For example, such prior known devices have employed means for bodily moving the entire coating or printing apparatus away from the mandrel so that there is no contact with the naked mandrel. Examples of such prior art devices include U.S. Pat. Nos. 4,441,418 and 4,491,613. While devices of the aforementioned type provide satisfactory operation when operated with equipment operating at relatively low speeds, they do not provide satisfactory operation in conjunction with modern high speed equipment due to the substantial amount of mass that must be moved during a deactivation operation and the fact that a large number of cans are lost for each skip-coat or skip-print operation.
Other prior known can printing devices such as that disclosed in U.S. Pat. No. 4,773,326 employ a plurality of blankets mounted on a rotary blanket wheel for pivotal movement about a trip pivot axis oriented parallel to the axis of rotation of the blanket wheel. In such apparatus detection of the absence of a container on a mandrel or the mispositioning of a container on a mandrel results in the deactivation of the blanket member that is approaching the printing position by causing the blanket assembly to be pivoted inwardly about the trip pivot axis so as to avoid contact with the mandrel as the blanket and the mandrel move into printing position. Additionally, the '326 patent also discloses another embodiment in which any empty mandrel is moved radially inwardly on its supporting turret to prevent contact with the printing blanket segment which the mandrel would otherwise contact in the printing station.
The concept of moving a mandrel radially inwardly by the use of complicated apparatus to effect a skip-print operation is also disclosed in U.S. Pat. Nos. 4,037,530 and 4,498,387. Similarly, U.S. Pat. No. 3,665,853 discloses a complicated linkage and cam follower arrangement for pivoting a blanket inwardly about a pivot axis extending parallel to the axis of rotation of the supporting member of the blanket. Similar skip-print means is shown in U.S. Pat. No. 3,563,170 in an offset printer/coater device.
The above-discussed prior art devices all suffer from being complicated, wear prone and expensive to maintain. The pivot shafts and bearings rely upon metal to metal sliding contact which results in wear so that frequent replacement of the wear-prone components is necessary in order to maintain the required accuracy for obtaining satisfactory printing results.
Another problem with prior can coating devices is that they frequently leave a visible color overlap line in the coating material on a can at the location at which the coating applying roller and the can separate at the end of the coating operation. During printing of can surfaces using prior art offset blanket procedures, the cans stay in contact with the blanket until the end of the blanket is reached. Ink on the blanket consequently gets pushed toward the end of the blanket so that there is an ink buildup which remains on the can at the moment of separation to cause a line of more intense color. Until the present time, there has been no way in which the intense color line could be avoided and it has simply been accepted by those of skill in the art. On the other hand, some conventional coaters employ a can positioned in rolling contact with a coating roll with the can being gradually removed from contact with the roll by rotation of the mandrel turret so that the can is gradually moved away from contact with the coating roll without there being an abrupt discontinuation of the application of coating material to the can Consequently, the overlap of the coating material is not as clearly visible as the overlap resultant from printing operations during the decorating of can bodies. The overlap of ink in a decorating operation is quite noticeable and is simply controlled to be about 1/8" wide. The foregoing problems and the use of a variable gravure roller as a proposed solution for some applications are disclosed in detail in U.S. Pat. No. 3,817,209. Other prior art patents have proposed the use of blanket segment sectors having tapered outer ends such as shown in U.S. Pat. Nos. 2,326,850 and 2,442,102. Published Japanese Patent Application No. 61-205 143 discloses coating in which the application roll and the container body are rotated at slightly different speeds to cause "slip" between the container and the roll to improve the coating quality.
Other problems which adversely affect the operation of can decorating equipment and other printing equipment are the problems of ink leakage from fountains and the problem of ink flow control for different equipment operating speeds necessary to achieve required color control for all speeds of operation. More specifically, ink fountains are used to meter the proper amount of ink into the system with the ink being smoothed and leveled and applied to one or more image plates on the plate cylinder in a uniform manner in order for proper operation. The image plates on the plate cylinder normally have a raised image which picks up ink from the inker and then transfers the ink onto the blanket surface in the desired pattern of the raised image. Most existing ink fountains leak excessively and manufacturers have apparently never been able to solve this problem. Most inkers employ side plates which are pressed against the end of the ink roll and an adjustable bottom blade which has an edge extending along the entire length of the roll. The cooperation of the side plates and the adjustable blade results in a space above the adjustable blade and between the side plates which contains the ink which is discharged onto the rotating roll through a very small space between the lower edge of the adjustable blade and the surface of the roll. Most of the adjustable blades are provided with a plurality of mounting screws engageable with the lower surface of such blades for deflecting the blade toward the roll to increase the blade pressure on the roll. Also, the side plates are pushed against the end of the roll in an effort to keep the ink from leaking outwardly beyond the side plates on the end surfaces of the roll. The action of friction between the blades and the roll causes the temperature of the ink to increase so as to reduce its viscosity and make it easier for leakage to occur.
The fountain roll is driven by a common power system with the rest of the printing apparatus so that speeding up of the printing apparatus results in a resultant speeding up of the speed of rotation of the fountain roll. Such an increase in the speed of the fountain roll should desirably result in an increase in the discharge of the ink to the ink train for deposit on the image plate in proportion to the additional ink required for printing the additional cans or other items; for example, if the ink fountain is supplying ink for the printing of cans at 500 cans per minute, an increase in production to 1000 cans per minute should result in a doubling of the amount of ink flow. Unfortunately, prior known devices do not operate in the necessary manner and frequently the ink flow increases more than is necessary due to the fact that the higher rotational speed causes deflection of the adjustable blade by an amount exceeding that necessary to simply keep up with the required increased ink requirements.
It has also been prior practice to employ various water circulation systems for cooling ink rollers in printing equipment. Such systems have been trouble prone and can create messy operating condition due to leaks particularly when the cooling water mixes with lubricants in the system.
Therefore, it is the primary object of the present invention to provide a new and improved can coating or printing apparatus and method.
A further object of the present invention is the provision of a new and improved container coating or printing apparatus having high speed stop-print capability.
Yet another object of the present invention is the provision of a new and improved stop-print offset printing means that is reliable, trouble free and highly accurate.
A further object of the present invention is the provision of a new and improved inker means that has greatly reduced ink leakage as compared to prior art devices.
Yet another object of the present invention is the provision of a new and improved inker blade adjusting means.
Yet another object of the present invention is the provision of a new and improved inker roll cooling means.